Proinflammatory and proapoptotic activities associated with Bordetella pertussis filamentous hemagglutinin

Filamentous hemagglutinin (FHA) is a dominant cell surface-associated Borde tella pertussis adhesin, Recognition that this protein is secreted in signi ficant amounts and that bacterial adhesins may have other activities, promp ted an assessment of FHA effects on human macrophages. Incubation of human macrophage like U937 cells with preparations of FHA resulted in dose-depend ent cytotoxicity, with death of 95% of treated cells after 24 h. Based on t he use of four independent methods, death of these cells could be largely a ttributed to apoptosis. FHA-associated apoptosis was also observed in THP-1 macrophage-like cells, fresh human peripheral blood monocyte derived macro phages (MDM), and BEAS-2B human bronchial epithelial cells. Infection of MD M with wild-type B. pertussis resulted in apoptosis within 6 h, while infec tion with an FHA-deficient derivative strain was only 50% as effective. FHA -associated cytotoxicity was preceded by host cell secretion of tumor necro sis factor alpha (TNF-alpha), a potential proapoptotic factor. However, pre treatment of cells with a neutralizing anti-TNF cy monoclonal antibody inhi bited only 16% of the FHA-associated apoptosis. On the other hand, a blocki ng monoclonal antibody directed against TNF-alpha receptor 1 inhibited FHA- associated apoptosis by 47.7% (P = 0.0001), suggesting that this receptor m ay play a role in the death pathway activated by FHA. Our in vitro data ind icate that secreted and cell-associated FHA elicits proinflammatory and pro apoptotic responses in human monocyte-like cells, MDM, and bronchial epithe lial cells and suggest a previously unrecognized role for this prominent vi rulence factor in the B. pertussis-host interaction.